Startup procedure for combined hydrofining-reforming process

ABSTRACT

A COMBINED HYDROFINING-DESULFURIZING-REFORMING SYSTEM IS BROUGHT ON STREAM RAPIDLY WHEN PROCESSING A FEED BOILING IN THE RANGE FROM 150* TO 450*F. AND CONTAINING SUBSTANTIALLY NO C3-C5 HYDROCARBONS, BY INTRODUCING MAKEUP C3-C5 HYDROCARBONS TO THE HYDROFINING ZONE OR DESULFURIZING ZONE AND PERMITTING THE C3-C5 HYDROCARBONS TO BE REFLUXED IN THE DESULFURIZING ZONE.

Jan. 19, 1971 A i BECK El AL 3,5563 STARTUP-PROCEDURE FOR-COMBINED HYDROFINING-REFORMING PROCESS Filed Sept. 29, 1969 REFORME DESULFURIZER q I v v E v 3 lNVENTORS 2 ROBERT R. BECK 1: HAROLD E. KNOWLTON CHARLESS.MCOV

VHlHdVN ATTORNEYS United States Patent 3,556,986 STARTUP PROCEDURE FOR COMBINED HYDROFINING-REFORMING PROCESS Robert R. Beck, Neptune Township, Monmouth County, and Harold E. Knowlton, Scotch Plains, N.J., and Charles S. McCoy, Orinda, Calif., assignors to Chevron Research Company, San Francisco, Calif., a corporation of Delaware Filed Sept. 29, 1969, Ser. No. 861,735 Int. Cl. C10g 23/00 US. Cl. 208-89 3 Claims ABSTRACT OF THE DISCLOSURE A combined hydrofining-desulfurizing-reforming system is brought on stream rapidly when processing a feed boiling in the range from 150 to 450 F. and containing substantially no C -C hydrocarbons, by introducing makeup C -C hydrocarbons to the hydrofining zone or desulfurizing zone and permitting the C -C hydrocarbons to be refluxed in the desulfurizing zone.

BACKGROUND OF THE INVENTION Field The present invention relates to a startup procedure for a refining process involving a hydrofining zone, a desulfurizing zone and a reforming zone.

Prior art Reforming of naphtha feeds to produce high-octane gasoline components is well known in the petroleum art. Generally the feed to a reforming zone is hydrofined in a hydrofining zone to reduce the sulfur impurities prior to contact with the catalyst in the reforming zone. The feed from hydrofining zone is generally fractionated in a desulfurizing-fractionating zone to separate produced H 8 and water from the naphtha which is to be reformed.

The startup of such a combined hydrofining-desulfurizing-reforming system has in the past generally involved up to a week or more. This delay in bringing the system to full severity results in the loss of valuable high-octane gasoline products.

SUMMARY OF THE INVENTION moval of water permits the reforming zone to be brought to high severity, that is, to reaction conditions wherein greater than 90 F-l clear gasoline can be produced, in a matter of several hours. Without the injection of the C -C hydrocarbons, the startup period of time would be several days to a week or more.

BRIEF DESCRIPTION OF THE DRAWING The present invention will be more fully explained hereinafter by reference to the figure which is a fiow schemeof a hydrofining-desulfurizing-reforming system.

DESCRIPTION OF THE INVENTION The combined process which is started up by the method of the present invention is basically a hydrofining zone; a desulfurizing-fractionating zone having a reflux stream wherein light gases are removed from the upper portion of the desulfurizing-fractionating zone, cooled and returned to the desulfurizing-fractionating zone; and a reforming zone.

Sulfur impurities in the feed to the hydrofining zone are therein converted to H 8. The reaction conditions in the hydrofining zone are generally operated at conditions resulting in substantially no cracking of the hydrocarbon feed to C -products. The effluent from the hydrofining zone is thereafter treated in the desulfurizing-fractionating zone to separate H 8 and Water from the hydrocarbon material. The hydrocarbon material, having little or no H 8 therein and being reduced in water content, is removed from the desulfurizing-fractionating zone and contacted in the reforming zone at reforming conditions to produce a high-octane gasoline product. In the reforming zone, particularly as the severity is increased, some light gas production, as Well as hydrogen production, occurs. The effluent from the reforming zone is thus treated to recover hydrogen and light gases, primarily C C hydrocarbons, from the gasoline stream, and a portion of this hydrogen stream containing C -C hydrocarbons is recycled to the hydrofining zone to supply the necessary hydrogen therefor.

The reforming zone may consist of one reactor or several reactors containing a hydrogenation-dehydrogenation catalyst. Preferably the reforming zone will comprise several reactors, preferably at least three reactors, in series. The hydrocarbon feed is preheated and mixed with hydrogen and then passed through the plurality of reaction zones containing catalyst. Generally in all but the last stages the reactions are endothermic; hence they hydrocarbon feed passing between each reaction zone is re heated to the desired conversion temperature. Reformed hydrocarbons are recovered from the terminal reactor and hydrogen is separated therefrom and a portion of the hydrogen recycled to the reforming reaction zones.

Reforming of the naphtha feedstock is generally accomplished at reaction conditions including a temperature within the range of from 600 to 1100 F., preferably from 750 to 1050 F. The pressure will generally vary from atmospheric to superatmospheric, preferably within the range from 25 to 1000 p.s.i.g., and preferably from 50 to 750 p.s.i.g. The temperature and pressure can be correlated with the liquid hourly space velocity (LHSV) to favor any particularly desirable reforming reactions, as, for example, aromatization or isomerization or dehydrogenation. In general, the liquid hourly space velocity will be from 0.1 to 10, and preferably from 1 to 5.

The reforming process is conducted in the presence of hydrogen. Hydrogen may be introduced from an extraneous source, e.g., pure hydrogen from bottles may be used. Thus, the hydrogen may be used only on a oncethrough basis. Inasmuch as reforming generally results in the production of hydrogen, hydrogen produced in the reaction may be separated from the reformate and recycled to the reaction zone, e.g., the first reactor in a series of reactors. Thus, extraneous hydrogen need not necessarily be added to the reforming process. However, if desired, extraneous hydrogen can be used at some stage of the operation, as, for example, during startup. Regardless of the source of the hydrogen, the hydrogen can be introduced into the feed prior to contact with the catalyst or can be contacted with the catalyst simultaneously with the introduction of feed to the reaction zone. The hydrogen need not necessarily be pure hydrogen, but may contain light hydrocarbon gases in admixture therewith. Generally, when hydrogen is recirculated to the reaction zone, light hydrocarbon gases will be recirculated with the hydrogen. It is preferred that relatively pure hydrogen be used; however, difiiculty and expense in purifying recycle hydrogen often prevents this from being the case. Hydrogen is preferably introduced into the reforming zone at a rate which varies from 0.5 to 20 moles of hydrogen per mole of feed.

The reforming conditions, as is obvious, will vary depending on the feed used, whether highly aromatic, paraffinic or naphthenic, and upon the desired octane rating of the product. Generally, it is preferred that the reforming process be operated at high severity conditions, that is, conditions which will result in the production of a gasoline product having at least 90 F-l clear octane rating, and preferably 95 F1 clear octane rating. Reforming at low severity, that is, at conditions which result in the production of gasoline of less than about 90 F-l clear octane rating, are generally necessary during the early periods of reforming, that is, when the feed is first being contacted with the reforming catalyst. As will be described further hereinafter, when the water content of the feed to the reforming zone exceeds about 30 p.p.m., it is very desirable that the reforming conditions be operated at low severity. Stated another way, when the partial pressure of water in the reaction zone is greater than about 0.02 p.s.i.a. (or, when the water content in the hydrogen recycle stream is greater than about 100 parts per million) and the severity of reforming is high, unfavorable sintering of the catalyst metal components occurs. Also, presence of excessive water at high severity conditions results in the removal of large amounts of halide from the catalyst, thereby rendering the catalyst less acidic than desired. As long as low severity conditions prevail, excessive water is not too detrimental to the catalyst.

The catalyst which finds use in reforming comprises a platinum group component associated with a porous solid carrier. Preferably the catalyst comprises a platinum group component, e.g., platinum, palladium, iridium, ruthenium, etc., supported with a porous inorganic oxide as, for example, alumina. The platinum group component will be present in an amount of from 0.01 to 3 Weight percent and preferably 0.01 to 1 Weight percent. The weight percent of a platinum group component is calculated as the metal regardless of the form in which it exists on the catalyst. The platinum group component embraces all the members of Group VIII of the Periodic Table having an atomic weight greater than 100 as well as compounds and mixtures of any of these. Platinum is the preferred component because of its better reforming activity.

Porous solid carriers which find particular use for reforming are generally the inorganic oxides, particularly inorganic oxides having surface areas of 50 to 750 m. gm., preferably 150 to 750 m. gm. The carrier can be a natural or a synthetically-produced inorganic oxide or combination of inorganic oxides. Typical acidic inorganic oxide supports which can be used are the naturally occurring aluminum silicates, particularly when acid treated to increase the activity, and the synthetically-produced cracking supports, such as silica-alumina, silica-zirconia, silicaalumina-zirconia, silica-magnesia, silica-alumina-magnesia, and crystalline zeolitic aluminosilicates.

It is generally preferred that the catalysts have low cracking activity, that is, have limited acidity. Thus, it is particularly preferred that alumina be present. Any of the forms of alumina suitable as a support for reforming catalysts can be used, e.g, gamma-alumina, eta-alumina, etc. Furthermore, alumina can be prepared by a variety of methods for purposes of this invention. Thus, the alumina can be prepared by adding a suitable alkaline agent such as ammonium hydroxide to a salt of aluminum, such as aluminum chloride, aluminum nitrate, etc., in an amount to form aluminum hydroxide which on drying and calcining is converted to alumina. Alumina can also be prepared by the reaction of sodium aluminate with a suitable reagent to cause precipitation thereof with the resulting formation of aluminum hydroxide gel. Also, alumina can be prepared by the reaction of metallic aluminum with hydrochloric acid, acetic acid, etc., in order to form a hydrosol which can be gelled with a suitable precipitating 4 agent, such as ammonium hydroxide, followed by drying and calcination.

Other components in addition to the platinum group component can be present with the porous solid carrier. It is particularly preferred that rhenium be present, for example, in an amount of from 0.01 to 5 weight percent and more preferably 0.01 to 2 weight percent. Regardless of the form in which rhenium exists on the catalyst, whether as metal or compound, the weight percent is calculated as the metal. Rhenium significantly improves the yield stability of the platinum-containing catalyst, that is, a process using a platinum-rhenium catalyst has a significantly lower yield decline throughout the reforming process than a catalyst comprising platinum without rhenium. The platinum-rhenium catalyst is more fully described in US. Pat. 3,415,737, which is incorporated herein by reference thereto.

The catalyst comprising the platinum group component can be prepared in a variety of methods; that is, the platinum group component can be associated with the porous solid carrier by impregnation, ion-exchange, coprecipitation, etc. Generally it is preferred to incorporate the platinum group component by impregnation. When rhenium is incorporated along with the platinum group component, the rhenium component can also be associated with the carrier by various techniques, e.g., impregnation, ionexchange, coprecipitation, etc. Preferably, the platinum group component and rhenium component are associated with the carrier by impregnation, either simultaneously or sequentially. Particularly preferred platinum group compounds for use in impregnation include chloroplatinic acid, ammonium chloroplatinates, polyammineplatinum salts, palladium chloride, etc. Suitable rhenium components are perrhenic acid, ammonium or potassium perrhenates, etc.

The catalyst used in reforming will preferably be promoted by the addition of halides, particularly fluoride or chloride. Bromides may also be used. The halides provide a limited amount of acidity to the catalyst which is beneficial to most reforming operations. A catalyst promoted With halide preferably contains from 0.1 to 3 weight percent total halide content. Halides can be incorporated onto the catalyst carrier at any suitable stage of catalyst manufacture, e.g., prior to or following incorporation of the platinum group component and/or the rhenium component. Halide can also be incorporated onto the catalyst during incorporation of the platinum group component or rhenium component.

The hydrofining Zone used in the combined process is generally operated at hydrofining conditions including a temperature of from 700 to 900 F., preferably from 700 to 850 F. Generally the pressure will fall Within the range from 200 to 2000 p.s.i.g., preferably 200 to 1000 p.s.i.g. The liquid hourly space velocity generally will be from 1 to 5, and th hydrogen/feed ratio will generally be from 1000 to 5000 or more s.c.f. hydrogen per barrel of feed. The reaction conditions are generally severe enough to convert substantially all the organic sulfur to hydrogen sulfide; thus the reaction conditions should be severe enough so that the effluent from the hydrofining zone contains less than about 10 p.p.m. organic sulfur, preferably less than about 1 p.p.m. organic sulfur. Generally the feed to the hydrofining zone will not contain substantial amounts of organic nitrogen; however, when nitrogen is present the organic nitrogen content may be reduced with the concurrent production of ammonia. The hydrofining reaction condtions should be such that substantially no cracking of the feed occurs. Thus, there should be substantially no C -production. Any cracking represents the loss of valuable gasoline-forming materials. By substantially no cracking is meant that less than about 5 Weight percent, preferably less than about 2 weight percent, of the feed is converted to C product (i.e., to C or lower boiling hydrocarbons).

The catalyst which finds use in the hydrofining zone will generally be cobalt-molybdenum, nickel-molybdenum or nickel-cobalt-molybdenum, supported on an alumina carrier or a zeolite carrier (for example, zeolite X, Y, L). Other supports or carriers may be used, e.g., silica, silica-alumina, magnesia, etc. A preferred catalyst for hydrofining or hydrodesulfurizing is an alumina-containing support with a minor portion of molybdenum oxide and cobalt oxide. The catalyst can be pretreated with hydrogen sulfide prior to contact with hydrogen and feed.

The desulfurizing-fractionating zone which finds use in the present invention is well known in the prior art. Basically the zone comprises a fractionation or distillation column having a series of plates or trays over which vapors rise toward the top of the column and liquid circulates downwardly. A stream is removed from the bottom of the column, reheated and returned to the bottom portion of the column. This provides the necessary heat input for operation of the system. If desired, a heating column could be placed at the bottom of the desulfurizing-fractionating column. The column is designed so that light gates, that is, H 8, water, and any light hydrocarbon gases boiling below the C range are removed from the top of the column. A portion of the light hydrocarbon gases thus removed is cooled and returned as liquid to the top portion of the column to provide the necessary reflux liquid. Unless a sutficient amount of light hydrocarbon gases, particularly C C hydrocarbons, are refluxed, the efficiency of the column for removing H 8 and water is decreased. It is obvious that inasmuch as the vapors leaving the top are cooled and returned as liquid to the column, only the hydrocarbon gases of the C C boiling range are effective reflux material. The difliculty in converting methane and ethane to a liquid removes these gases as possible choices.

The hydrocarbon effiuent from the desulfurizing-fractionating zone which is substantially free of H 8 and water and light hydrocarbon gases is then passed to the reforming zone. Unless the desulfurizing-fractionating zone is properly refluxed, water will not be removed in substantial amounts.

The present inventive startup procedure disclosed and claimed herein is valuable when processing feeds boiling within the range from l50-450 F. and containing substantially no light hydrocarbon gases (i.e., less than about 1 weight percent). The feeds boiling within the naphtha range may be straight-run naphthas or thermally cracked or catalytically cracked naphthas or blends thereof. The present invention is particularly useful when the feed to the hydrofining zone contains organic sulfur compounds in an amount of at least 100 ppm. and water or compounds which will form water in an amount of at least 50 ppm. The feed to the reforming zone should contain less than about ppm, more preferably less than 1 p.p.m., sulfur, either organic sulfur or H 3, etc. Thus the hydrofining zone must convert substantially all of the organic sulfur in the feed to H 8, and the desulfurizing-fractionating zone must operate efficiently enough to remove substantially all the H 5 from the feed. Also, inasmuch as the refolming zone cannot be brought to high severity until the Water content in the feed to the reforming zone is less than about ppm, it is necessary that the desulfurizing-fractionating zone remove substantially all the water therein. Any compounds which will form water are generally converted to water in the hydrofining zone.

As indicated previously, the reformer must be operated at low severity until the water content to the feed in the reformer is low, that is, below about 30 ppm. The desulfurizing-fractionating zone which removes water in the feed from the hydrofining zone operates efliciently only if adequately refluxed with C -C hydrocarbons. But since the hydrofining zone is operated at conditions wherein substantially no cracking occurs and the feed originally contains no C -C hydrocarbons, a difficulty is presented as far as adequately refluxing the desulfurizing-fractionating zone. Generally when the combined system is operating at high severity, that is, particularly when the reforming zone is operating at high severity C -C hydrocarbons are produced in the reforming zone and are recycled to the hydrofining zone and thence to the desulfurizing-fractionating zone. However, the reforming zone does not produce substantial amounts of C -C hydrocarbons until high severity is reached, and high severity cannot be reached until the water content in the feed is reduced; thus, the end result is normally a slow startup procedure, requiring up to a week or more before suflicient C -C hydrocarbons are recycled from the reforming zone to the hydrofining zone and thence to the desulfurizing-fractionating zone, thereby allowing adequate refluxing of the desulfurizing-fractionating zone to take place.

The slow startup procedure of the prior art can be considerably shortened by the addition of makeup C C hydrocarbons either to the feed to the hydrofining zone or to the feed to the desulfurizing-fractionating zone.

Thus the addition of hydrocarbons boiling in the range of C -C hydrocarbons in the amount of from 1 to 10 Weight percent, based on the total hydrocarbon feed to the hydrofining zone, will permit rapid startup of the over-all process. The excess C -C hydrocarbons are refluxed in the desulfurizing-fractionating zone, thereby permitting eflicient removal of water from the feed to the reforming zone. By C -C hydrocarbons, it is meant to include such hydrocarbons as propane, butane, isobutane, pentane, isopentane, etc., or mixtures thereof.

The process of the present invention will be better un derstood by reference to the diagram in the figure. The diagram shows a typical combined hydrofining/desulfurizing-fractionating/reforming system wherein the present invention is applicable. A naphtha feed boiling within the range of from l50-450 F. and containing at least ppm. organic sulfur compounds and at least 50 ppm. water (or compounds which will form water) and containing substantially no C -C hydrocarbons is introduced through line 1, in contact with hydrogen from line 2, thence through line 3 to furnace 4. The naphtha feed and hydrogen are heated in furnace 4 to hydrofining reaction conditions and are then passed by line 5 into hydrofining reaction zone 6 containing hydrofining catalyst 7, preferably a cobalt oxide-molybdenum oxide-alumina catalyst. In the hydrofining zone 6 the organic sulfur compounds are converted to H S; also any compounds which will form water are converted to water at the reaction conditions. The total eflluent from hydrofining zone 6 is passed by line 8 to separation zone 9. In separation zone 9 hydrogen is removed by line 10 and the hydrocarbon feed containing the H 5 and H 0 is passed by line 11 to desulfurizing-fractionating column 12.

The light hydrocarbons, that is the hydrocarbons boiling in the C -C range and lower, plus H 5 and water are removed from the top of the desulfurizing-fractionating column 12 by line 13, cooled in heat exchanger 14, then passed by line 15 to separation zone 16. Light gases such as methane and ethane, H S and water, are removed by line 17; the heavier hydrocarbons. that is, the C -C hydrocarbons, are returned as liquid by line 18 t0 the desulfurizing-fractionating column 12.

From the bottom of desulfurizing-fractionating column 12 heavy hydrocarbons, that is, hydrocarbons boiling from C and above, are removed by .line 19. A portion of the heavier hydrocarbons is generally returned to the desulfurizing-fractionating column 12 by line 20 through furnace 21 and line 22. This reflux of heavy hydrocarbons provides suflicient heating to operate the column, i.e., to permit vaporization of at least part of the liquid moving down the column.

The purified effluent from desulfurizing-fractionating column 12 is passed by line 19 t0 reforming furnace 23.

Hydrogen may be added to the feed at this stage as desired (not shown). The feed exiting from furnace 23 by line 24 will generally be at the temperature for reforming. The feed is passed to the reforming reactor 25 and con acted with a hydrogenation-dehydrogenation catalyst 26. Preferably the catalyst comprises a platinum group component, particularly platinum in association with alumina. The preferred catalyst is platinum-rhenium associated with alumina. In reforming reactor 25 the hydrocarbon naphtha is reformed to high octane gasoline components which is removed by line 27 and passed to separator 28. In separator 28 hydrogen and light gases which were produced in reforming reactor 25 are separated from the gasoline boiling range materials.

The gasoline product is passed from separator 28 by line 29 to debutanizer 31 wherein a high-priority product stream is removed by line 31 and a light gas stream is removed by line 32. I

The hydrogen and light hydrocarbons, particularly the C -C hydrocarbons, recovered from separator 28 are passed by line 33, admixed with the hydrogen from line 10, and thence by line 2 to admixture with the naphtha feed to the hydrofining zone. A portion of the hydrogen gas recovered in separator 28 may be bled oil by line 34 and used as a fuel or used in a hydrocracking zone, etc.

During startup of the present combined process and until sufiicient C C hydrocarbons are produced in the reforming zone for recycle to the hydrofining zone and desulfurizing-fractionating zone, makeup C -C hydrocarbons can be introduced into desulfurizing-fractionating zone 12 or into the reflux system or at any convenient point before the desulfurizing-fractionating zone 12. It is particularly preferred that the makeup C C hydrocarbons be introduced into the feed to the hydrofining zone, for example by line 35. At least 1 to weight percent C -C hydrocarbons, based on the total feed, can be introduced, based on the total feed, can be introduced by line 35. Alternately, C -C hydrocarbons can be added to the feed from the hydrofining zone, e.g., via line 36.

If more hydrocarbon feed is hydrofined than can be used in the reforming zone, the excess hydrofined feed can be stored for a period of time. The excess feed may then later on be added to the stream to the desulfurizingfractionating zone as a makeup hydrofined hydrocarbon stream (not shown in the figure). The C -C hydrocarbons can be introduced with this makeup hydrofined hydrocarbon stream, if desired.

The foregoing description of this invention is not to be considered as limiting since many variations can be made by those skilled in the art Without departing from the spirit or scope of the appended claims.

What is claimed is:

1. In a combined hydrofining-reforming system:

wherein a hydrocarbon feed boiling Within the range from l50450 F. (and containing substantially no C -C hydrocarbons) and containing organic sulfur compounds in an amount of at least 100 p.p.m. and Water or compounds which will form Water in an amount of at least 50 ppm. is contacted in a hydrofining zone at hydrofining conditions and in the presence of hydrogen with a catalyst to convert organic sulfur compounds to H 8 with substantially no cracking to C -product,

and the effluent from the hydrofining zone is treated in a desulfurizing-fractionating zone to separate H 5 and water from the hydrocarbon material,

and a reflux stream of light gases is removed from the upper portion of the desulfurizing-fractionating zone, cooled and returned to the desu1furizing-fractionating zone,

and the efiluent (hydrocarbon material) from the desulfurizing-fractionating zone is contacted in a reforming zone at reforming conditions and in the presence of hydrogen with a reforming catalyst to produce a product of high octane rating,

and the effluent from the reforming zone is separated into at least a hydrogen stream normally containing C -C hydrocarbons and a gasoline stream, at least a portion of the hydrogen stream being recycled to the hydrofining zone,

the improvement for rapidly bringing the combined process onstream which comprises introducing makeup C -C hydrocarbons to the feed to the hydrofining stream or to the feed to the desulfurizing-fractionating zone, and permitting the C -C hydrocarbons to be refluxed, the weight percent of C C hydrocarbons to total hydrocarbon feed being from 1 to 10.

2. The process of claim 1 wherein said reforming catalyst comprises platinum in association with the porous solid carrier, said platinum being present in an amount from 0.01 to 3 weight percent.

3. The process of claim 1 wherein the product of high octane rating from the reforming zone has an octane number of at least F-l clear octane.

References Cited UNITED STATES PATENTS 3,109,804 11/1963 Martin 20889 3,122,495 2/1964 Rosenblatt et al. 20897 DELBERT E. GANTZ, Primary Examiner R. BRUSKIN, Assistant Examiner US. Cl. X.R. 208134 *zg gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,556 .986 Dated Januarv 19. 1971 Inventr(s) ROBERT P.- BECK et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2, line 7 "c -oroducrs" should read --C products-- Col. H line 70 "C -production" should read --C production-.

Col. line 7 "C -oroduct" should read --C product-.

Col. 8 line 9 "C -product," should read --C product,--

Signed and sealed this 1 0th day of August 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR Attesting Officer Commissioner of Patents 

